• Journal of the Korea Computer Industry Society
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• v.4 no.4
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• pp.523-532
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• 2003

In this paper, we designed a 128-bit block cipher, Lambda, which has 16-round extended Feistel structure and analyzed its secureness by the differential cryptanalysis and linear cryptanalysis. We could have full diffusion effect from the two rounds of the Lambda. Because of the strong diffusion effect of the algorithm, we could get a 8-round differential characteristic with probability $2^{-192}$ and a linear characteristic with probability $2^{-128}$. For the Lambda with 128-bit key, there is no shortcut attack, which is more efficient than the exhaustive key search, for more than 8 rounds of the algorithm.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.28 no.6
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• pp.1379-1392
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• 2018

The complexity of the differential-linear cryptanalysis is strongly influenced by the probability of the differential-linear characteristic computed under the assumption of round independence, linear approximation independence, and uniformity for the trail that does not satisfy differential trail. Therefore, computing the exact probability of the differential-linear characteristic is a very important issue related to the validity of the attack. In this paper, we propose a new concept called DLCT(Differential-Linear Connectivity Table) for the differential-linear cryptanalysis. Additionally, we propose an improved probability computation technique of differential-linear characteristic by applying DLCT. By doing so, we were able to weaken linear approximation independence assumption. We reanalyzed the previous results by applying DLCT to DES and SERPENT. The probability of 7-round differential-linear characteristic of DES is $1/2+2^{-5.81}$, the probability of 9-round differential-linear characteristic of SERPENT is computed again to $1/2+2^{-57.9}$, and data complexity required for the attack is reduced by $2^{0.2}$ and $2^{2.2}$ times, respectively.

• ETRI Journal
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• v.36 no.6
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• pp.1032-1040
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• 2014

The Lai-Massey scheme, proposed by Vaudenay, is a modified structure in the International Data Encryption Algorithm cipher. A family of block ciphers, named FOX, were built on the Lai-Massey scheme. Impossible differential cryptanalysis is a powerful technique used to recover the secret key of block ciphers. This paper studies the impossible differential cryptanalysis of the Lai-Massey scheme with affine orthomorphism for the first time. Firstly, we prove that there always exist 4-round impossible differentials of a Lai-Massey cipher having a bijective F-function. Such 4-round impossible differentials can be used to help find 4-round impossible differentials of FOX64 and FOX128. Moreover, we give some sufficient conditions to characterize the existence of 5-, 6-, and 7-round impossible differentials of Lai-Massey ciphers having a substitution-permutation (SP) F-function, and we observe that if Lai-Massey ciphers having an SP F-function use the same diffusion layer and orthomorphism as a FOX64, then there are indeed 5- and 6-round impossible differentials. These results indicate that both the diffusion layer and orthomorphism should be chosen carefully so as to make the Lai-Massey cipher secure against impossible differential cryptanalysis.

• Journal of Platform Technology
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• v.11 no.1
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• pp.72-84
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• 2023

With the rise of the Internet of Things, the security of such lightweight computing environments has become a hot topic. Lightweight block ciphers that can provide efficient performance and security by having a relatively simpler structure and smaller key and block sizes are drawing attention. Due to these characteristics, they can become a target for new attack techniques. One of the new cryptanalytic attacks that have been attracting interest is Neural cryptanalysis, which is a cryptanalytic technique based on neural networks. It showed interesting results with better results than the conventional cryptanalysis method without a great amount of time and cryptographic knowledge. The first work that showed good results was carried out by Aron Gohr in CRYPTO'19, the attack was conducted on the lightweight block cipher SPECK-/32/64 and showed better results than conventional differential cryptanalysis. In this paper, we first apply the Differential Neural Distinguisher proposed by Aron Gohr to the block ciphers HIGHT and GOST to test the applicability of the attack to ciphers with different structures. The performance of the Differential Neural Distinguisher is then analyzed by replacing the neural network attack model with five different models (Multi-Layer Perceptron, AlexNet, ResNext, SE-ResNet, SE-ResNext). We then propose a Related-key Neural Distinguisher and apply it to the SPECK-/32/64, HIGHT, and GOST block ciphers. The proposed Related-key Neural Distinguisher was constructed using the relationship between keys, and this made it possible to distinguish more rounds than the differential distinguisher.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.12 no.4
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• pp.77-85
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• 2002

We present the impossible differential cryptanalysis of the block cipher XTEA[7] and TEA[6]. The core of the design principle of these block ciphers is an easy implementation and a simplicity. But this simplicity dose not offer a large diffusion property. Our impossible differential cryptanalysis of reduced-round versions of XTEA and TEA is based on this fact. We will show how to construct a 12-round impossible characteristic of XTEA. We can then derive 128-bit user key of the 14-round XTEA with $2^{62.5}$ chosen plaintexts and $2^{85}$ encryption times using the 12-round impossible characteristic. In addition, we will show how to construct a 10-round impossible characteristic or TEA. Then we can derive 128-bit user key or the 11-round TEA with $2^{52.5}$ chosen plaintexts and $2^{84}$ encryption times using the 10-round impossible characteristic.

• Journal of the Korea Institute of Military Science and Technology
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• v.14 no.2
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• pp.238-245
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• 2011

We suggest a DES key expansion algorithm which is strong enough to overcome Differential Cryptanalysis(DC) and Linear Cryptanalysis(LC). Checking the weak points of DES, we found that the opened S box provide all information on the various kinds of attack. Using the key expansion we redesigned the S box which is not open to anybody who has no key. DC and LC can not be applied to the suggested algorithm without the redesigned S box information. With the computer experiments we show that the efficiency of this algorithm is almost the same as that of DES with respect to the crypto speed.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.5 no.1
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• pp.25-36
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• 1995

Differential Cryptanalysis(DC) and Linear Cryptanalysis(LC) are considered to be efficient attack methods which could be applied to DES and other DES-like private key Cryptosystems. This paper analyzes the DC and LC attack to DES and design a 80-bit block Cipher (80-DES) which could be strong against DC and LC Attack.

• ETRI Journal
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• v.23 no.4
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• pp.158-167
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• 2001

We examine the diffusion layers of some block ciphers referred to as substitution-permutation networks. We investigate the practical and provable security of these diffusion layers against differential and linear cryptanalysis. First, in terms of practical security, we show that the minimum number of differentially active S-boxes and that of linearly active S-boxes are generally not identical and propose some special conditions in which those are identical. We also study the optimal diffusion effect for some diffusion layers according to their constraints. Second, we obtain the results that the consecutive two rounds of SPN structure provide provable security against differential and linear cryptanalysis, i.e., we prove that the probability of each differential (resp. linear hull) of the consecutive two rounds of SPN structure with a maximal diffusion layer is bounded by $p^n(resp.q^n)$ and that of each differential (resp. linear hull) of the SDS function with a semi-maximal diffusion layer is bounded by $p^{n-1}(resp. q^{n-1})$, where p and q are maximum differential and linear probabilities of the substitution layer, respectively.

• Journal of the Korea Society of Computer and Information
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• v.13 no.4
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• pp.169-175
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• 2008

The existing block encryption algorithms have been designed for the encryption key value to be unchanged and applied to the round functions of each block. and enciphered. Therefore, it has such a weak point that the plaintext or encryption key could be easily exposed by differential cryptanalysis or linear cryptanalysis, both are the most powerful methods for decoding block encryption of a round repeating structure. Dynamic cipher has the property that the key-size, the number of round, and the plaintext-size are scalable simultaneously. Dynamic network is the unique network satisfying these characteristics among the networks for symmetric block ciphers. We analyze the strength of Dynamic network for meet-in-the-middle attack, linear cryptanalysis, and differential cryptanalysis. Also, In this paper we propose a new network called Dynamic network for symmetric block ciphers.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.15 no.1
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• pp.77-86
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• 2005

Related-Cipher attack was introduced by Hongjun Wu in 2002. We can consider related ciphers as block ciphers with the same round function but different round number and their key schedules do not depend on the total round number. This attack can be applied to block ciphers when one uses some semi-equivalent keys in related ciphers. In this paper we introduce differential related-cipher attacks on block ciphers, which combine related-cipher attacks with differential cryptanalysis. We apply this attack to the block cipher ARIA and SC2000. Furthermore, related-cipher attack can be combined with other block cipher attacks such as linear cryptanalysis, higher-order differential cryptanalysis, and so on. In this point of view we also analyze some other block ciphers which use flexible number of rounds, SAFER++ and CAST-128.